1. Field of the Invention
The present invention relates to an image reading apparatus and reading method, and particularly relates to an image reading apparatus and reading method in which the enlargement or reduction ratio of the image can be set over a wide range.
2. Description of the Related Art
In generally, a conventional image reading apparatus can enlarge or reduce the image read from an original document, which is the object to be read, within a range of, for instance, 65-154%.
When enlarging or reducing the image read from an original document in this way, the scanning speeds of the image reading unit in both the main scanning direction and the secondary scanning direction must be altered. This is carried out by altering the moving speed of the image reading unit for the secondary scanning direction, which is the direction of paper transport, and by altering the position of the optical lens for the main scanning direction.
Moreover, an in recent years, image reading apparatus using digital methods have has been developed. This image reading apparatus can execute enlargement or reduction of the image read from the original document within the range of 50-400%.
In the conventional apparatus which enlarges or reduces images read from original documents within the range of 50-400%, data read in the main scanning direction can be electrically processed to effectively alter the scan rate. However, the secondary scanning direction is processed by altering the moving speed of the image reading unit.
For instance, when enlarging the image read from the original document to a magnification of 400%, the image reading unit moving speed becomes 1/4 of that when the magnification is 100%. Since the frequency of the clock pulse for synchronizing the stepping motor which moves the image reading unit also becomes 1/4, the image reading unit itself approaches its mechanical inherent frequency. As a result of this, the image reading unit itself nears or enters a state of resonance. This causes such problems as the generation of abnormal noise or the occurrence of randomness in the copied image.
Moreover, when the magnification is small, for example with magnification 50%, the image reading unit moving speed becomes greater. The stepping motor driving frequency for moving the image reading unit also becomes high. As a result, not only is discordant noise generated, but also there is the disadvantage that the moving torque at this time diminishes.